Blending FG to the MDF

After countless hours of reading, I'm finally ready to start on some fiberglassing projects.  One thing still puzzles me, but maybe I'm just thinking about it too hard.  When making an encloser or any other piece that has a large flat spot, MDF should be used.  Now, after the fleece has been stretched around the piece and fastened to the back of the MDF, won't there be a "high spot"?  I guess what I am getting at is the fact that if you put a level across the piece of MDF, the FG portion will not allow the part to sit level on a flat surface.  What is done to correct this?

Say yo' if you raised up your speaker ring then you shouldnt have any flat spots.Can you elaborate a little more on the prob.

                   Uncle gumby

You need to use your router.  Use a rabbit bit (?).  Router around the edges, this will give you a place to staple your fleece.  Then you just need to bring the lower edge up to the top edge by using the fiberglass and resin.  Larry Jr